I have seen these things in the past, and want to use them myself, but don't know what they are called to even find them.

Basically how they work is the larger PCB has holes that are larger than the male pin and a little metal insert goes in there and gets soldered in. Then the male pin header gets inserted in there so the connection is much more lower profile than the traditional female socket header.

 

They are called pin receptacles.



https://www.digikey.com/en/products...4IgTCBcDaIA4EsB2ACATgUwMYbgFwEMsAbDAZxAF0BfIA

 

What about PIN headers?
https://www.amazon.ca/Glarks-Connector-Assortment-Stackable-Breakaway/dp/B07CWSXY7P/ref=sr_1_1_sspa?crid=2W9AQTGMDA899&keywords=header+pins&qid=1688306590&sprefix=header+pins,aps,106&sr=8-1-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&psc=1

 

Pin headers are the non-low profile method I have been using. With these the PCB boards when stacked are 13mm from each other. Some of it from the male header, but most of it from the female.

Pin receptacle from that link do fit my description, but I remember seeing even simpler (and probably cheaper) versions where the receptacle was just made from some bent sheet metal. And the pin was visible on the other side of the PCB once inserted into the receptacle.

 

Are these what you mean?
https://www.harwin.com/products/H2175-05/
https://www.harwin.com/products/H3183-01/

 

https://www.digikey.com/en/products/detail/harwin-inc/S9091-46R/5175731

They looked sort of like this, except they hugged the pin from all side, were smaller, and I doubt cost 0.27 cents a piece.

 

Or is there a better way to join 2 PCBs populated with SMDs together, that is low profile? Given that I'm making only one of the PCBs. The other has rows of through holes.

 

These are very low profile, SMD headers and sockets.

 

You can achieve the same thing with right-angled male and female headers.

 

You can achieve the same thing with right-angled male and female headers.

View attachment 297539
View attachment 297538

I don’t know if you were referring to the connectors I linked. They are a little misleading. They are designed to be stacking connectors, the flat end is soldered to the PCB, so they are vertical.

 

You can achieve the same thing with right-angled male and female headers.

I have some boards that have 2 rows of pins, like say a NodeMCU breakout for an ESP8266, that I didn't think it would be possible to do that, but now that I thought about it for a little longer, if the angled headers are both facing the same way, it could slide into place.

There will be some wasted space on the board from one of the headers that will be outside the dimensions of the "daughter-board", but given how cheap these are due to economies of scale, I just might well give that a try.